In an oil-impregnated sintered bearing having pores into which lubricating oil is impregnated, a shaft which is inserted into the sintered bearing is rotated, and an oil pressure is thereby generated in the lubricating oil existing in a small gap between the shaft and a sliding surface which is an inner peripheral surface of the sintered bearing. The shaft is thereby supported by this oil pressure with high accuracy. However, in the condition of the sintered bearing, leakage of the lubricating oil is inclined to occur from a surface other than the sliding surface of the sintered bearing. In particular, the leakage of the lubricating oil easily occurs from an end surface of the sintered bearing, which is exposed on the outside thereof. When the leakage of the lubricating oil occurs, the oil pressure thereof decreases. Due to this, direct contact of the shaft and the bearing often occurs, frictional resistance increases and durability decreases.
In order to solve the above problems, a technique was conceived in which a sealing process is performed for sealing pores exposed on an end surface of the sintered bearing. For example, methods therefor have been proposed in which high frequency vibration is supplied to an end surface of a sintered bearing (see Japanese Unexamined Patent Application Publication No. Hei 8-33260 and Japanese Unexamined Patent Application Publication No. Hei 11-51055).